Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field
  • G02F1/166—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field characterised by the electro-optical or magneto-optical effect
  • G02F1/167—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field characterised by the electro-optical or magneto-optical effect by electrophoresis
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field
  • G02F1/1675—Constructional details
  • G02F1/1676—Electrodes
  • G02F1/16762—Electrodes having three or more electrodes per pixel
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field
  • G02F1/1675—Constructional details
  • G02F1/1679—Gaskets; Spacers; Sealing of cells; Filling or closing of cells
  • G02F1/1681—Gaskets; Spacers; Sealing of cells; Filling or closing of cells having two or more microcells partitioned by walls, e.g. of microcup type
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field
  • G02F1/1685—Operation of cells; Circuit arrangements affecting the entire cell

Definitions

• the present invention relates to an electrophoretic display device.
• the electrophoretic display apparatus includes an electrophoretic display device constituted by a pair of substrates disposed with a spacing therebetween, an insulating liquid filled in the spacing, colored electrophoretic particles (charged migration particles) dispersed in the insulating liquid, and a display electrode disposed along each of the substrates.
• the colored electrophoretic particles are electrically charged positively or negatively, so that they are deposited on either one of the display electrodes depending on a polarity of a voltage applied to the display electrode.
• the colored electrophoretic particles are deposited on the upper (display) electrode to provide a visible state of the colored electrophoretic particles or on the lower (display) electrode to provide a visible state of the insulating liquid.
• the electrophoretic display device includes: a dispersion liquid comprising positively charged black electrophoretic particles 11, negatively charged white electrophoretic particles 12, and an insulating liquid in which the black and white electrophoretic particles 11 and 12 are contained; Electrodes, comprising a first electrode 15 and a second electrode 16, for forming an electric field in the dispersion liquid by applying a voltage between the electrodes; an insulating layer 17 for separating the dispersion liquid 10 and the first electrode 15; an insulating layer 18 for separating the dispersion liquid 10 and the second electrode 16; and a partition wall for partitioning adjacent pixels.
• a relaxation time constant of accumulated electric charges by drive of respective parts is different depending on physical properties of respective constitutional members.
• the relaxation time constant is defined as a product of an electric resistance and an electrostatic capacity (capacitance) of each part when an equivalent electric circuit is considered on the basis of an electric field generated by each part.
• the relaxation time constant of the dispersion liquid 10 is a product of a resistance and a capacitance of the dispersion liquid 10, thus being in agreement with a product of a volume resistivity and a dielectric constant of the dispersion liquid 10.
• a DC component in drive of the electrophoretic display device by applying one-polarity voltage, i.e., a positive voltage or a negative voltage, a DC component remains in the electrophoretic display device, so that there arises such a problem that a voltage applied at the time of writing and an effective voltage applied to the electrophoretic particles 11 and 12 are different from each other.
• a base color of the electronic paper is white, so that the electrophoretic display device is strongly required to permit writing from white display reset.
• An interparticular attraction force determined by values of surface energy of the electrophoretic particles 11 and the dispersion liquid 10 is weaker than an attraction force, exerted between the electrophoretic particles 11 and the partition wall 7A, determined by values of surface energy of the electrophoretic particles 11, the dispersion liquid 10, and the partition wall 7A. Accordingly, the state in which the electrophoretic particles 11 are deposited in the plurality of layers is unstable, so that the deposition state is changed by a slight change in electric field strength (intensity) . As a result, an optical response characteristic in writing from white display reset is changed abruptly. In other words, the particles deposited state is changed even by the slight change in electric field strength to unstabilize a resultant optical response characteristic.
• a principal object of the present invention is to provide an electrophoretic display device having solved the above described problems.
• a specific object of the present invention is to provide an electrophoretic display device capable of alleviating accumulation of residual DC component and stabilizing an optical gradation level in writing from white display reset.
• an electrophoretic display device comprising: a first substrate and a second substrate which are disposed with a spacing therebetween, a partition wall disposed in the spacing, electrophoretic particles sealed in a closed space , defined by the first and second substrates and the partition wall, in which a distribution state of the electrophoretic particles is changed to effect display, a first electrode disposed at a side surface of the closed space, and a second electrode disposed at a bottom surface of the closed space, wherein the first electrode has an area substantially equal to or larger than an area of the second electrode.
• the first electrode disposed at a side surface of the closed space and the second electrode disposed at a bottom surface of the closed space have the substantially same area, whereby it becomes possible to perform such a drive that an opposite polarity voltage is alternately applied between the respective electrodes even in the case of repetitively performing display rewriting, thus alleviating remarkably the accumulation of the residual DC component. Further, by providing the first electrode with a larger area than that of the second electrode, it is possible to stabilize an optical gradation level in writing from white display reset.
• Figure 1 is a perspective view showing a pixel structure of an electrophoretic display device according to First Embodiment of the present invention
• Figures 2(a) and 2(b) are sectional views each showing electric line of force at each pixel of the electrophoretic display device.
• Figures 3(a) and 3(b) are graphs each showing an electrooptical characteristic of the electrophoretic display device.
• Figure 4 is a time chart for illustrating a drive sequence for effecting bipolar reset.
• Figure 5 is a sectional view showing a pixel of an electrophoretic display device according to Second Embodiment of the present invention.
• Figure 6 is a perspective view showing a pixel of an electrophoretic display device according to Third Embodiment of the present invention.
• Figure 7 is a top view of the pixel of the electrophoretic display device shown in Figure 6.
• Figures 8(a) and 8(b) are perspective view each showing pixel (s) of an electrophoretic display device according to Fourth Embodiment of the present invention.
• Figure 9 is a sectional view showing an embodiment of a structure of a conventional electrophoretic display device.
• Figure 10 is a sectional view showing a state at the time of white display reset in a conventional horizontal movement-type electrophoretic display device .
• Figure 1 is a schematic perspective view showing a pixel structure of an electrophoretic display device according to this embodiment.
• the electrophoretic display device includes a pixel G, a first substrate 1, a second substrate 2 disposed opposite to the first substrate 1 with a spacing therebetween, a partition wall 7 for keeping the spacing between the first and second substrates 1 and 2 at a predetermined distance and partitioning the pixel and an adjacent pixel, a closed space defined by the first and second substrates 1 and 2 and the partition wall 7, a liquid-phase forming electrophoretic dispersion liquid 3 in which a liquid-phase dispersion medium and charged electrophoretic particles (not shown) dispersed in the dispersion medium are sealed, a second electrode 5 formed on the second substrate 2, and a first electrode 4 formed at a surface of the partition wall 7.
• the electrophoretic display device in the embodiment is a matrix panel having 600x1800 pixels.
• Each pixel G has a height A of 20 ⁇ m, a width B of 40 ⁇ m, and a length (depth) C of 120 ⁇ m.
• the first electrode 4 is formed at surfaces of a pair of partition wall 7 portions constituting a pair of opposite side surfaces. In this embodiment, two opposite side surfaces of four side surfaces and a bottom surface of the pixel G is coated with the electrodes (the first and second electrodes 4 and 5) .
• Each of the respective electrodes 4 and 5 is surface-coated with an insulating layer 6.
• As the electrophoretic particles contained in the electrophoretic dispersion liquid 3 which is sealed in the closed space are black particles.
• the dispersion medium contained in the dispersion liquid 3 isoparaffin is used and, as the electrophoretic particles, particles of polystyrene-polymethyl methacrylate copolymer (resin) (particle size: 1 - 2 ⁇ m) containing carbon black are used.
• a thin film transistor (TFT) is formed and connected with a voltage application circuit, thus constituting an electrophoretic display apparatus .
• the first and second electrodes 4 and 5 have the same depth dimension (length) C and the first electrode 4 is divided into two portions which are formed at opposite two surfaces of adjacent partition wall portions 7, an area of the first electrode 4 means a sum of areas of these (first electrode) two portions 4.
• the pixel G has a ratio of A (height) :B (width) of 1:2, so that the first electrode 4 and the second electrode 5 have the same area.
• a distribution of electric field strength is substantially symmetrical with respect to the electrode surfaces of the first electrode 4 and the second electrode 5.
• the electric field strength varies depending on a position and has a distribution but a manner of the distribution from a maximum to a minimum on the first electrode surface is substantially identical to that on the second electrode surface.
• the electric field strength on the first electrode 4 is stronger with a shorter distance from the first substrate 1 and is weaker with a longer distance from the first substrate 1.
• the electric field strength on the second electrode 5 is stronger at a portion closer to the partition wall 7 and is weaken at a pixel center portion.
• the electric field strength is determined by a distance from a bonding (contact) portion of the partition wall 7 and the first substrate 1. Accordingly, as apparent from the ratio A:B of 1:2, the distribution of electric field strength on the first electrode 4 is substantially identical to that on 1/2 of the entire second electrode 5. Actually, the first electrode 4 contacts the second substrate 2 but the half of the second electrode 5 is connected with the other half of the second electrode 5.
• the optical response characteristic in writing from white display reset is substantially identical to that in writing from black display reset, so that it is possible to perform reset operation by alternately changing a polarity between a positive side and a negative side at the same voltage amplitude and perform writing at voltages of both of the polarities.
• FIG 4 is a time chart showing a drive sequence for effecting bipolar reset of the electrophoretic display device of this embodiment.
• a voltage Vrw is applied so as to effect white display reset and then an arbitrary gradation is written.
• a voltage Vrb is applied so as to effect black display reset and then an arbitrary gradation is written.
• the voltages Vrw and Vrb have the same amplitude but have opposite polarities.
• the first electrode 4 and the second electrode 5 with the same area, it becomes possible to equalize the electric field strength exerted on the electrophoretic particles in writing from white display reset to that in writing from black display reset. As a result, it is possible to perform bipolar-voltage drive using positive and negative voltages (of both polarities) . Further, even in the case of repeating display rewriting, it becomes possible to perform such a drive that the respective electrodes are alternately supplied with voltages of opposite polarities, so that accumulation of the residual DC component can be remarkably alleviated compared with a conventional monopolar-voltage drive and it is possible to remedy the burn-in problem.
• FIG. 5 is a schematic sectional view of a pixel of an electrophoretic display device according to this embodiment, wherein the same reference numerals as in Figure 1 represent the same or corresponding portions.
• black electrophoretic particles 11 are contained in an electrophoretic dispersion liquid 3.
• a pixel G has a height (A) of 60 ⁇ m, a width (B) of 40 ⁇ m, and a length or depth (C) of 60 ⁇ m ( Figure 1) .
• a length in a height direction of the pixel G is longer than a length in a width direction.
• the electrophoretic particles 11 are deposited in the plural layers on a cell deposition surface at the time of white display reset and the particle deposition state is charged by the slight change in electric field strength, thus resulting in a problem of unstable optical response characteristic.
• the electrophoretic particles 11 at the time of white display reset are deposited in a single layer on the cell deposition surface as shown in Figure 5 because of the larger height (A) of the pixel G.
• electrophoretic particles When the electrophoretic particles are preset at the electrode surface in such a state that they are deposited in the plurality of layers, electrophoretic particles directly contacting the electrode have a strong deposition force but electrophoretic particles located at an upper portion of the plurality of layers thereof have a weak deposition force, thus being suspended in the dispersion liquid by a slight oscillation or shaking.
• electrophoretic display device one of the causes of an unstable collected state of electrophoretic particles on the partition wall compared with an extended state of electrophoretic particles on the substrate may be attributable to the deposition state of electrophoretic particles in the plural layers.
• the particle deposition state is table and is less liable to be changed by the slight change in electric field strength, so that the optical characteristic of the electrophoretic display device is not largely changed by a slight change in applied voltage. Accordingly, compared with the conventional electrophoretic display device, the electrophoretic display device of this embodiment can stabilize an optical gradation level in writing from white display reset and improve a controllability in gradation writing from the white display reset.
• the electrophoretic particles 11 are placed in such a deposition state that they are deposited in the single layer in white display reset.
• the area of the first electrode 4 may preferably be not more than approximately three times the area of the second electrode 5.
• FIG. 6 is a schematic perspective view of a pixel of an electrophoretic display device according to this embodiment, wherein the same reference numerals as in Figure 5 represent the same or corresponding portions.
• a pixel G has a height (A) of 10 ⁇ m, a width (B) of 40 ⁇ , and a length or depth (C) of 40 ⁇ m, and four side surfaces and a bottom surface of the pixel G are coated with electrodes. More specifically, in this embodiment, at four side surfaces (including two pairs of opposite surfaces) , the first electrode 4 is disposed.
• the thickness of the insulating layer 6 of the second electrode 5 is made larger at four corners of the pixel G where the electric field strength is stronger and made smaller at a pixel center portion where the electric field strength is weaker, whereby it becomes possible to perform bipolar drive at the same drive voltage.
• a distance from the first electrode 4 to the surface of the insulating layer 6 thereon and a distance from the surface of the insulating layer 6 thereon are made equal to each other, and when an intersection line is taken as a line of intersection of an extended plane of the first electrode surface and an extended plane of the second electrode surface, a distance from the intersection line to an edge of the first electrode surface closest to the intersection line and a distance from the intersection line to an edge of the second electrode surface closest to the intersection line are made equal to each other.
• the electric field strength exerted on the electrophoretic particles is symmetrical with respect to the white display reset and the black display reset.
• the optical response characteristic is improved compared with the conventional one, thus resulting in the above described electrooptical characteristic as shown in Figure 3(a).
• the optical response characteristics in writing from the white display reset and from the black display reset are substantially identical to each other, thus permitting the bipolar reset operation.
• the opposite-polarity reset can be performed alternately to realize such a drive that the residual DC component is less liable to accumulate. As a result, it is possible to effect stable display rewriting with less occurrence of the burn-in.
• FIG. 8(a) and 8(b) are schematic perspective view of a pixel of an electrophoretic display device according to this embodiment, wherein the same reference numerals as in Figure 1 represent the same or corresponding portions.
• a side surface electrode 8 for preventing an electric field generated by a first electrode 4 and a second electrode 5 from adversely affecting adjacent pixels is disposed at opposite two side surfaces of four side surfaces of a pixel G. More specifically, in this embodiment, of the four side surfaces of the pixel G, the side surface electrode 8 is disposed at opposite two side surfaces and the first electrode 4 is disposed at other opposite two side surfaces. These four side surfaces and a bottom surface of the pixel G are coated with electrodes (the first and side surface electrodes 4 and 8 and the second electrode 5) .
• the pixel G has a height (A) of 20 ⁇ , a width (B) of 40 ⁇ m, and a length (depth) (C) of 60 ⁇ m as shown in Figure 8(a), so that an areal ratio between the side surface electrode 8 and the first electrode 4 is 2:3.
• the influence of the side surface electrodes 8 can be reduced. As a result, it becomes possible to perform drive of the electrophoretic display device only by the first electrode 4.
• the first electrode 4 has a substantially rectangular shape but may be a substantially triangular shape or a substantially polygonal shape.

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• Physics & Mathematics (AREA)
• Nonlinear Science (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
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• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Molecular Biology (AREA)
• Electrochromic Elements, Electrophoresis, Or Variable Reflection Or Absorption Elements (AREA)

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• 2004
  • 2004-06-07 JP JP2004169112A patent/JP4708739B2/ja not_active Expired - Fee Related
• 2005
  • 2005-06-06 US US10/553,264 patent/US7423800B2/en not_active Expired - Fee Related
  • 2005-06-06 WO PCT/JP2005/010737 patent/WO2005121885A1/en not_active Ceased
• 2008
  • 2008-07-28 US US12/180,667 patent/US8259062B2/en not_active Expired - Fee Related

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